1. Field of the Invention
The present invention generally relates to tools for use in oil and gas well operations, and more particularly to improved bumper spring tools for use in oil and gas wells.
2. Background of the Invention and Description of the Prior Art
A newly drilled and completed well typically has enough pressure within the formation to cause liquids in the formation and the well to flow to the surface without aid. Over time, however, as the well's production volume and bottom-hole pressure decline the liquids fall back on the perforations—the passages into the formation—thus creating what is called a “loaded well” condition. In this condition the well no longer has sufficient pressure to cause the liquids to flow to the surface without some artificial lift.
A plunger lift is a type of artificial lifting device utilized in oil and gas wells to efficiently unload liquids. The system usually requires no external energy to provide the necessary pressure to lift the liquids to the surface, instead relying on the residual pressure in the well to lift the plunger. The gas-to-liquid ration required varies depending on many conditions. The common rule of thumb used in the industry is 300 to 400 scf per barrel per 1000′ of depth.
FIG. 1 illustrates a conventional oil and gas well fitted with a plunger lift system for controlling production, including generic plunger lift and bumper spring devices typical of the prior art. The system illustrated in FIG. 1 typically comprises the following structures. A well 10 is formed by a casing 12 that lines the well 10. Within the casing 12 is a tubing string 14 that encloses the well bore 16 through which oil or gas 30 is produced from a formation 18 through perforations 20. Within the well bore 16 is a bumper spring assembly 22 resting on a seating nipple 24 (which may also be called a tubing or collar stop). A lift or bypass plunger 26, shown traveling upward under the pressure of the fluids and/or gas in the well bore 16, pushes or lifts a “slug” of fluid 32 ahead of it. The well 10 includes the wellhead apparatus 42 disposed on the surface of the earth 40 for directing the production of the well to appropriate receptacles or pipelines (not shown).
A bumper spring assembly is a tool that is typically placed in a seating nipple at the lower end of the tubing in the well to absorb the momentum of the bypass or lift plunger as it reaches the seating nipple, thereby protecting the seating nipple from damage. Structurally, most bumper springs comprise a shaft or mandrel, a head piece at the upper end and a cage attached to the lower end. The head piece and cage are typically threaded onto the mandrel and secured with a pin to prevent the rotation of the end piece with respect to the mandrel so that the bumper spring becomes disassembled. Other methods to prevent loosening of the end pieces include welding and lock nuts.
Conventional plungers do not readily fall through flow within the well, so the well must be closed to stop the flow so that the plunger will fall to the bottom of the well due to gravity, contacting the bumper spring at the bottom. The fall speed of such plungers (which include pad, brush, solid, sand, spiral, etc.) typically ranges from 50 to 400 feet/minute. Newer types of plungers (such as bypass, continuous run, flow-through, ball & sleeve, sliding sleeve, etc.) are designed for falling through flowing liquids to enable substantially high production from the well. This performance is provided by features such as passages or ports machined into the body of the plunger or its cage to permit liquid flow. However, the rate of fall of these plungers may reach velocities as high as 2000 feet/minute. The greater momentum of such plungers places much greater stress on the pinned components of the bumper spring. This is a serious disadvantage because the pins are frequently sheared, resulting in loosening of the components of the bumper spring. The head piece or cage may become unscrewed, allowing loose pieces to travel up and down the well depending on the flow of the well. Damage to the plunger, the well casing or other structures may result; in other cases the plunger may become stuck in the well bore, lodged there by pieces that become wedged between the plunger and the well bore. This causes the well to be shut down while the problem is repaired, causing a substantial loss of production.
Conventional bumper spring assemblies may also impede the flow of production because of their position within the well bore, often in the path of fluids entering the well bore from the perforated regions of the well casing.
Accordingly there is a need for an improved bumper spring assembly that survives many high-velocity cycles in the well bore and presents minimal obstruction to the flow of production facilitated by the bypass or lift plunger used to restore production.